The present invention generally relates to a polarimeter and, in particular, relates to one such polarimeter having a plurality of polarizing optical fibers.
In many modern processes, such as the formation of thin films on optical substrates, for example, rugate filters, antireflection coatings and the like, the status of the process is monitored by measuring the change in light polarization. Depending on the particular application, the change in light polarization of interest can either be the change between the known polarization of an incident light beam and the polarization of a reflected light beam or the change between the known polarization of an incident light beam and the polarization of a light beam transmitted through the workpiece. Hence, by relating the change in the polarization of either the reflected or transmitted light to the parameters of the particular process, the process can be monitored.
Typically, this type of process monitoring is performed by an instrument generally known as an ellipsometer. As known in the art, conventional ellipsometers include a complex assembly of rotating polarizers, angle sensing encoders and drive motors. As the polarizers are rotated, the polarization of the light either reflected or transmitted from the workpiece is modulated. Further, such ellipsometer are so large that they must be located outside the vacuum chamber wherein the process is actually taking place. Hence, it becomes necessary to get a polarized light beam in and out of a vacuum system, which in turn introduces added complexity into both the device and analysis. Further, the use of the principles of the ellipsometer are limited due to the size and complexity of the instrument. Thus, the applications for using ellipsometers as well as the principles thereof are quite limited.
Consequently, since a change in the polarization of reflected, transmitted, or even sampled ambient light can be related to known events, it is highly desirable to provide an apparatus and technique that is more versatile than conventional polarization monitoring instruments.